The present invention generally relates to an improved method and apparatus for measuring the properties of thermoset plastics and viscoelastic materials, and more specifically to method and apparatus for sealing thermoset plastics and viscoelastic materials during testing thereof.
In the prior art, there are many well known instruments for determining various properties of viscoelastic materials (e.g., rubber and like materials). These instruments include such apparatus commonly referred to as Moving Die Rheometers (MDR), Rubber Process Analyzers (RPA), Oscillating Disk Rheometers (ODR), and Mooney Viscometers. These instruments apply a rotational shear strain to a sample material and measure the resulting torque. It should be understood that the applied rotational shear may be oscillatory or continuous. In the case of an MDR or RPA, a sample material to be tested is enclosed in a cavity formed between two opposing die plates, and the rotational shear is applied to the sample by rotating one die plate, while the other die plate remains stationary, and the torque required to apply the shear is measured. In the case of an ODR or Mooney Viscometer sample material to be tested is enclosed in a cavity formed between two opposing die plates, rotational shear is applied to the sample material by means of a rotor embedded in the sample, and the torque required to apply the shear is measured. In U.S. Pat. Nos. 3,479,858; 4,343,190; and 4,552,025, the force is applied by rotation of one die plate relative to the other, and the measurements made are of the torque required to apply the shearing force or of the torque induced in the second die plate (reaction torque) when the first (driven) die plate is rotated. It should be noted that testing of sample materials is typically a period of 1 minute to 24 hours.
An exemplary prior art instrument is shown in FIG. 1. It should be appreciated that a variety of other similar instruments, such as those noted above, are also suitable for use in connection with the present invention. Apparatus A1 includes members 1, 2 and 3, which are respectively left and right vertical and horizontal components of an outer frame which is supported on a base (not shown). A lower die assembly comprising a lower die housing 4 and a housing 5 for a drive shaft 6, is mounted in the horizontal member 3. Drive shaft 6 is connected at its upper end to a lower die plate (not shown). An inner frame, which is located beneath horizontal member 3 has vertical portions 7 and 8, and a lower horizontal portion 9. Tie rods 10 and 11, which pass through horizontal member 3, are attached at their lower ends to a lower crosshead 13. An upper die assembly, comprising an upper die housing 14, is mounted in an upper crosshead 12. A pneumatic cylinder 15 mounted beneath the horizontal portion 9 of the inner frame has a cylinder rod 16 which is connected to the lower crosshead 13. Actuation of pneumatic cylinder 15 causes the assembly consisting of a cylinder rod 16, lower crosshead 13, tie rods 10, 11 and upper crosshead 12 to travel downwards, thus bringing upper die housing 14, lower die housing 4, and the die plates into the closed position. The drive system to the lower die plate includes a computer controlled electric motor 17, mounted with its output shaft 18 coaxial with drive shaft 6 to the lower die plate. The two shafts 18, 6 are coupled by means of a sleeve 19.
General operation of a typical instrument for measuring the properties of viscoelastic materials is as follows: The two opposing die plates are first moved to an open position, so that a sample of viscoelastic material can be placed between the die plates. In some cases the sample will be sandwiched between layers of film. Next, the two opposing die plates are moved to a closed position to form a test cavity, wherein the sample of viscoelastic material is maintained under pressure. The temperature of the die plates is controlled during the measurement process. The sample is then subjected to an oscillating, rotary shear force having a predetermined amplitude and frequency. A torque is measured, which is indicative of the response of the sample to the shearing force. Information is derived on the properties of the material from such measurements. It should be appreciated that the shear force is applied to the sample by rotation of one die plate relative to the other. The torque measurements are the torque required to apply the shearing force or of the torque induced in the second die plate (reaction torque) when the first die plate (driven) is rotated. It should be appreciated that other suitable arrangements are also possible.
While the instruments described above are suitable for testing relatively high viscosity rubbery viscoelastic materials, several problems are encountered when such instruments are used to test relatively low viscosity materials, such as thermoset plastics (e.g., resins). One of these problems relates to containment of the low viscosity sample material within the die cavity. If too much sample material flows out of the die cavity when pressure is applied to the sample material in the die cavity, an appropriate torque measurement cannot be made. In this regard, if there is an insufficient gripping of the sample material as the shearing force is applied, the torque measurements will be invalid.
Another problem relates to bonding of low viscosity sample materials to components of the test instrument outside the die cavity. In this respect, low viscosity materials such as thermoset plastics are good adhesives, and when they set up they harden and bond to surfaces. This may occur during a curing procedure. Adherence to components such as sealing plates, will distort torque measurements. This problem is referred to as xe2x80x9cgrounding.xe2x80x9d
Accordingly, there is a need for a method and apparatus that will contain a low viscosity test material within a die cavity and prevent grounding.
According to the present invention there is provided a containment system comprising: (a) a first die assembly including a first die plate having a first diameter; (b) a second die assembly including a second die plate rotatable relative to said first die plate and having the first diameter, wherein said first and second die assemblies are movable between an open and closed position, said first and second die plates forming a die cavity for holding a sample material; and (c) a sealing means located between said first and second die plates to inhibit release of the sample material from the die cavity.
According to another aspect of the present invention there is provided a method for inhibiting the release of a sample material from a die cavity of a test instrument for measuring properties of the sample material, wherein said die cavity is defined by first and second die plates which are movable between an open and closed position, said method comprising: moving the first and second die plates to the open position; locating a generally annular seal means between said first and second die plates; locating the sample material within an opening bounded by said seal means; and moving said first and second die plates to a closed position, wherein said seal means is compressed therebetween by the peripheral edges of said first and second die plates or sealing plates.
An advantage of the present invention is the provision of a containment system for inhibiting the release of low viscosity test material from a die cavity during testing thereof.
Another advantage of the present invention is the provision of a containment system for inhibiting the release of low viscosity test material from a die cavity when the test material is pressurized.
Still another advantage of the present invention is the provision of containment system for inhibiting the release of low viscosity test material from a die cavity when the test material is in a melt phase.
Yet another advantage of the present invention is the provision of containment system for inhibiting low viscosity test material in a die cavity from contacting mechanical components of the test instrument outside the die cavity.
Yet another advantage of the present invention is the provision of containment system for inhibiting the release of low viscosity test material a die cavity, and adhering to mechanical components of the test instrument outside the die cavity when the test material is in a cure phase.
Still other advantages of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description, accompanying drawings and appended claims.